Metallic nanoparticles have been the subject of extensive research due to their unique optical, electronic, and molecular-recognition properties. They have applications in a wide variety of areas, including chemical analysis, medical diagnosis and environmental monitoring. Metallic nanoparticles are emerging as promising biosensors because of their unique properties and ability to interact with biomolecules. For example, metallic nanoparticles have been explored for the detection of oligonucleotides, proteins and cells.
US 2005/0059042 A1 describes a method of oligonucleotide detection utilizing gold nanoparticles with either single stranded (ss) or double stranded (ds) deoxyribonucleic acid (DNA). Electrostatic interactions were used to distinguish between ssDNA and dsDNA because ssDNA adsorbs on gold and prevents their aggregation in a salt solution while dsDNA does not prevent aggregation. This aggregation leads to color change and thus, ssDNA remains pink while dsDNA turns blue. This method is limited to oligonucleotides and requires the use of salt for aggregation of nanoparticles.
US 2008/0268450 A1 describes a method of detecting proteins using surface modified magnetic nanoparticles along with gold nanoparticles. The magnetic nanoparticles are modified with antibodies against the protein of interest as well as specific oligonucleotide sequences. The gold nanoparticles are modified with complimentary oligonucleotide sequence. The protein of interest is first concentrated by separation using the magnetic nanoparticles. These particles are then complexed with the gold nanoparticles and detection is performed using thin layer chromatography (TLC) chips. This approach requires the use of a magnet for protein separation and also additional TLC chips for separation of gold nanoparticles. Thus, several steps are involved in detection.
WO 2012/139122 A1 describes a gold nanoparticle-based colorimetric assay for detecting nucleic acids from viral, bacterial and other microorganisms in clinical specimens using unmodified gold nanoparticles and specific oligotargeter polynucleotides that bind to the pathogen-specific nucleic acids.
US 2012/0302940 A1 describes functionalized gold nanoparticles for use in the treatment of cancer cells and pathogenic bacteria. In this case, the nanoparticles were modified with specific oligonucleotides or antibodies that would bind to cancer cells or bacteria. The cells were characterized using Raman spectroscopy before and after photothermal treatment. The absence of a Raman spectrum after treatment demonstrated the effectiveness of the treatment at killing the respective cells. This technique requires the use of a specific label for the cells and also a Raman spectrometer for quantification of the cells.
Methods employing modified metallic nanoparticles can suffer from several disadvantages. For example, different functionalized nanoparticles are required for different targets; separation of ligands for functionalizing nanoparticles (such as DNA) can be costly; covalent conjugation of bioactive ligands onto the surface of nanoparticles could reduce their reactivity. Furthermore, methods employing modified nanoparticles can be time-consuming, require numerous reagents and steps, and require expensive equipment and/or specialized expertise.
It is desirable to provide detection methods using metallic nanoparticles that do not require modification. In particular, it is desirable to provide a simple method for the detection of pathogens using unmodified metallic nanoparticles.